The gross federal debt
The gross federal debt y (in trillions of dollars) for a certain country in year x is approximated by the following equation, were x is the number of years after 2000.
y=0.9x+6.04
In what year will the federal debt be 19.54 trillion?
y = 0.9x + 6.04
19.54 = 0.9x + 6.04
0.9x + 6.04 = 19.54
0.9x = 19.54 - 6.04
0.9x = 13.5
x = 13.5 / 0.9
x = 15
That would be in the year 2015